Direct expansion evaporator with vapor ejector capacity boost

ABSTRACT

A system and method for increasing the refrigeration capacity of a direct expansion refrigeration system having a vapor separator and a vapor ejector. After the throttling process at the expansion device, the mixture of liquid and vapor enters the inlet separator. The vapor separator generates vapor to power the ejector through flashing of warm refrigerant liquid from a higher temperature and pressure to a lower pressure. The cooler refrigerant liquid then goes to the evaporator coil inlet. Furthermore, the system stabilizes the superheat of the outlet vapor and reduces fluctuations in outlet superheat caused by excess unevaporated liquid flowing from the outlets of the tubes due to mal-distribution at the inlet.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to direct expansion refrigeration systems.

SUMMARY OF THE INVENTION

One of the drawbacks of direct expansion (DX) refrigeration technologywhen compared to pump overfeed systems is the reduction in coolingcapacity due to the reduction in liquid refrigerant flow through theevaporator to achieve the superheat at the evaporator outlet.

The present invention is an improvement on current technology DXevaporators such that heat absorbing capacity is increased by increasinglocalized refrigerant flow. The liquid refrigerant flow is increasedthrough local recirculation of liquid from evaporator outlet toevaporator inlet through a vapor ejector which pumps liquid refrigerantfrom a lower pressure to a higher pressure. This ejector is powered bythe flash gas generated in the expansion device before the evaporatorinlet.

The invention features a vapor ejector and separator combination thatutilizes the flash gas generated from throttling to recycle additionalrefrigerant liquid from the evaporator outlet to the evaporator inlet.The flash gas generated in DX systems can vary from 5 to 15% or more ofthe total mass flow rate entering the evaporator. The flash gas isconsidered mostly a parasitic loss since it does not play a role in theevaporation process (the liquid refrigerant is the key player). Thisinvention enables employing the above flash gas to increase the capacityof the evaporator by recirculating additional liquid through theevaporator. The increased liquid improves heat transfer through higherinternal surface contact with boiling liquid. The technique is aregenerative method which utilizes flash gas to boost capacity.

The invention includes a vapor-liquid separator and a vapor ejector.After the throttling process, as in a standard refrigeration cycle, themixture of liquid and vapor enters the inlet vapor-liquid separator. Thevapor-liquid separator generates vapor to power the ejector throughflashing of warm refrigerant liquid from a higher temperature andpressure to a lower pressure. The cooler refrigerant liquid then goes tothe evaporator inlet as in a normal DX system. The refrigerant vapor asthe motive flow travels through the vapor ejector. The vapor ejectorpulls cold refrigerant liquid from the outlet of the evaporator into theside port of the ejector. The cold refrigerant liquid and motive vaporflow are separated at the ejector outlet. The liquid is returned to theevaporator inlet circuits for evaporation. The motive vapor flow isreturned to the evaporator outlet connection. An expansion valveresponsive to refrigerant vapor superheat, after the point where coldrefrigerant liquid is collected, would typically be used to adjust inletliquid flows to the evaporator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representation of a standard direct expansion refrigerationsystem.

FIG. 2 is a representation of a direct expansion evaporator with vaporejector capacity boost according to an embodiment of the invention.

FIG. 3 is a representation of a direct expansion evaporator with vaporejector capacity boost according to another embodiment of the invention.

FIG. 4 is a representation of a direct expansion evaporator with vaporejector capacity boost according to another embodiment of the invention.

FIG. 5 is a representation of a direct expansion evaporator with vaporejector capacity boost according to another embodiment of the invention.

Features in the attached drawings are numbered with the followingreference numerals: 3 expansion device. 33 ejector 5 expansion deviceoutlet 35 ejector liquid inlet 7 refrigerant line 37 ejector outlet 9inlet to evaporator inlet separator 39 refrigerant line 11 inletvapor-liquid separator 41 outlet separator inlet 13 inlet separatorvapor outlet 43 outlet vapor-liquid separator 15 inlet separator liquidoutlet 45 outlet separator liquid outlet 16 refrigerant line 46refrigerant line 17 distributor inlet 47 outlet separator vapor outlet18 refrigerant line 49 refrigerant line 19 distributor 50 liquid headerinlet 20 distributor side port 51 liquid header 21 distributor outlet 53liquid header first outlet 23 evaporator inlets 55 liquid header secondoutlet 25 evaporator 57 refrigerant line 26 refrigerant line 59 outletseparator second inlet 27 evaporator outlet 100 superheat sensor 29refrigerant line 102 controller 30 refrigerant line 31 ejector vaporinlet

DETAILED DESCRIPTION

FIG. 1 shows a typical or standard direct expansion (DX) refrigerationsystem. High pressure, high temperature liquid from high pressurereceiver enters the evaporator through a thermostatic expansion valveand a distributor. The thermostatic expansion valve regulates (opens orcloses) based on the superheat of the outlet vapor with the goal ofgenerating superheated vapor (superheat ≥6° F.) to ensure dry suctionfor the compressor. However, this is not the case in practice, asunevaporated liquid tends to escape the evaporator resulting inreduction in superheat and closing of the thermostatic expansion valveto reduce the refrigerant flow rate. This reduces refrigerationcapacity. Furthermore, there is also a need for a suction trap as shownin FIG. 1 to trap any liquid and ensure dry suction to the compressor.

A DX system as described above, which uses a distributor to distributeliquid to all circuits of the evaporator is also sensitive tomal-distributions. Non-uniform distribution results in excess liquidflowing out of some circuit outlets, which will reduce superheat belowtarget. This causes the thermostatic expansion valve to increasesuperheat back to target at the cost of reduced capacity.

FIG. 2 shows the portion of a DX refrigeration system of the inventionwhich replaces the portion of a prior art DX refrigeration system thatis enclosed in dashed lines in FIG. 1 . Referring to FIG. 2 , highpressure, high temperature subcooled liquid is delivered to expansiondevice 3. The outlet 5 of the expansion device 3 is connected viarefrigerant line 7 to the inlet 9 of a vapor-liquid separator 11 (alsoreferred to herein as inlet separator), which sends vapor flash gasreceived from the expansion device to inlet 31 of an ejector 33, whileliquid refrigerant is sent to the inlet 17 of distributor 19 viarefrigerant line 16. Distributor outlets 21 are connected to theevaporator coil 25 via refrigerant line 26 for delivery of refrigerantliquid to the evaporator coil 25. While an evaporator coil is used as anexample herein, any type of evaporator may be used in connection withthe invention. Outlet 27 of the evaporator coil 25 produces bothsuperheated vapor and unevaporated liquid. The superheated vapor is sentto the suction trap and/or compressor via refrigerant line 29, and theunevaporated liquid is sent to the liquid inlet 35 of the ejector 33 viarefrigerant line 30. Sensor 100 measures the temperature and pressure ofthe superheated vapor and sends it to controller 102 to determinewhether superheat has been achieved. Controller 102 causes the expansiondevice to open or close depending on the superheat determination.

Meanwhile, ejector 33 uses the flash gas received from the outlet 13 ofinlet separator 11 to cool the unevaporated liquid, and the outlet 37 ofthe ejector 33 delivers the cooled refrigerant liquid and excess flashgas to the inlet 41 of a vapor-liquid separator 43 (also referred toherein as outlet separator) via refrigerant line 39. The outletseparator 43 separates the vapor from the liquid and sends the liquidback to the evaporator coil 25 via a liquid outlet 45 and correspondingrefrigerant line 46. Vapor leaves outlet 47 and joins the vapor leavingthe outlet 27 of the evaporator coil 25 via refrigerant line 49.According to this arrangement, the DX system of the invention mayprovide excess liquid to the evaporator coil in order to maximizerefrigeration capacity, but excess liquid leaving the evaporator coil iscaptured, redirected and reheated before being re-delivered to theevaporator coil, thereby preventing damage to the compressor.

FIG. 3 shows a variation of the embodiment shown in FIG. 2 , in whichthe liquid outlet 45 from the outlet separator 43 connected to a sideport 20 of the distributor 19 via refrigerant line 46.

FIG. 4 shows an alternate embodiment in which the distributor 19 of theembodiment shown in FIG. 2 is replaced with a liquid header 51.According to this embodiment, inlet separator 11 sends liquidrefrigerant to the inlet 50 of liquid header 51 via refrigerant line 16.Liquid header has first outlets 53 and a second outlet 55. First outlets53 are connected directly or indirectly to the evaporator coil 25, andsecond outlet 55 is connected to a second inlet 59 of the outletseparator 43 via refrigerant line 57 for providing additional excessliquid to the outlet separator 43. As with the embodiment of FIG. 2 ,the outlet 45 of outlet separator 43 is connected to the inlet 23 ofevaporator coil 25 via refrigerant line 46.

FIG. 5 shows a variation of the embodiment shown in FIG. 4 in whichoutlet 45 of outlet separator 43 is connected directly to the liquidheader 51 via refrigerant line 46.

While the inlet vapor-liquid separator, the ejector, and the outletvapor-liquid separator are shown in the exemplary figures anddescription as constituting separate structure elements, they may beoptionally combined into an integrated refrigerant recycling devicewhich carries out the functions of all three devices.

1. An apparatus for improving the performance of a direct expansionrefrigeration system, the apparatus comprising: an inlet separatoradapted to be connected to an expansion device outlet of said directexpansion refrigeration system, an evaporator connected to a liquidoutlet of said inlet separator, an ejector connected to a vapor outletof said inlet separator, a first refrigeration line connecting an outletof said evaporator to a liquid inlet of said ejector, a secondrefrigeration line connecting said outlet of said evaporator to acompressor, said inlet separator configured to simultaneously andcontinuously deliver refrigerant vapor to said ejector and refrigerantliquid to said evaporator.
 2. A direct expansion refrigeration systemcomprising: a refrigerant line connecting the following, in order: anexpansion device, an inlet separator, an evaporator, and a compressor,said refrigeration system further comprising an ejector connected to anoutlet of said inlet separator and to an outlet of said evaporator, saidinlet separator configured to simultaneously and continuously deliverrefrigerant vapor to said ejector and refrigerant liquid to saidevaporator.
 3. A direct expansion refrigeration system according toclaim 1, wherein said inlet separator and said ejector are combined inan integrated refrigerant recycling device.
 4. A method for increasingthe refrigeration capacity of a direct expansion refrigeration systemwithout risking liquid refrigerant damage to a compressor comprising thefollowing steps, simultaneously: taking liquid from an outlet of anevaporator and delivering it to an ejector, taking refrigerant vaporfrom an inlet separator located upstream of an evaporator and deliveringit to said ejector, using said ejector to warm said refrigerant liquidreceived from said evaporator with said vapor received from said inletseparator, and taking all liquid from said ejector and delivering it tosaid evaporator.
 5. A direct expansion refrigeration system according toclaim 2, wherein said inlet separator and said ejector are combined inan integrated refrigerant recycling device.
 6. A method according toclaim 4, further comprising taking refrigerant liquid from said inletseparator and delivering it directly to a distributor for saidevaporator.
 7. A method according to claim 4, further comprising takingrefrigerant liquid from said inlet separator and delivering it to anevaporator liquid header.
 8. A direct expansion refrigeration system ofclaim 2, further comprising a heat exchanger connected to said expansiondevice to deliver cooled refrigerant to said expansion device.